This invention relates to a fuel injector for use in supplying fuel under pressure to a combustion space of an internal combustion engine. In particular, the invention relates to a fuel injector in which a characteristic of the fuel injector can be altered, in use.
In order to reduce the levels of noise and particulate emissions produced by an engine it is desirable to provide an arrangement whereby the injection characteristics of fuel delivered to the engine can be controlled. For example, it may be desirable to be able to adjust the spray pattern formed by the delivery of fuel by an injector or to adjust the rate of fuel injection. British Patent Application GB 2 307 007 A and European Patent Application EP 0 713 004 A describe fuel injectors of the type in which the fuel injection characteristic can be varied, in use, by selecting different sets of fuel injector outlet openings provided in the fuel injector nozzle body. In both of these fuel injector designs, by controlling angular motion of a sleeve member, housed within the nozzle body, apertures formed in the sleeve are caused to align with selected ones of the outlet openings. Subsequent inward, axial movement of a valve member within the bore of the nozzle body causes fuel to be ejected from the selected outlet openings. Fuel injectors of this type do, however, have performance limitations.
Additionally, European Patent Application No. 00301922.1 describes a fuel injector including a nozzle body defining a bore within which an outwardly opening, outer valve member is slidable. Movement of the outer valve member in an outward direction causes fuel to be ejected from an upper group of outlet openings provided in the outer valve member. The outer valve member defines a blind bore within which an inner valve needle is slidable. Inward movement of the inner valve needle causes fuel injection through a lower group of outlet openings provided in the outer valve member. The fuel injection rate is controlled by means of an actuator arrangement which controls the downward force applied to the inner valve needle. A fuel injector of this type does, however, suffer from the disadvantages of outwardly opening fuel injectors. For example, a poor spray characteristic is obtained as the outlet openings become exposed and, in addition, fuel leakage can occur from the outlet openings during undesirable stages of the fuel injection cycle.
U.S. Pat. No. 5,588,412 describes a fuel injector of the inwardly opening type including a nozzle body provided with outlet openings which occupy different axial positions. Fuel injection through different ones of the outlet openings is selected by controlling axial movement of a spool valve. However, the fuel injector has the disadvantage that a high rate of fuel leakage through the outlet openings can occur during undesirable stages of fuel injector operation.
It is an object of the present invention to provide an alternative fuel injector which enables the fuel injection characteristics to be varied, in use and which alleviates at least some of the disadvantages of known fuel injectors having this capability.
According to the present invention, there is provided a fuel injector comprising a nozzle body having a bore therein, within which first and second valve needles are slidable, the first valve needle being engagable with a first seating to control fuel injection from a first outlet opening provided in the nozzle body, the second valve needle being engagable with a second seating to control fuel injection from a second outlet opening provided in the nozzle body, the fuel injector further comprising first and second control chambers for fuel, whereby fuel pressure within the first and second control chambers controls movement of the first and second valve needles away from their respective seatings so as to permit fuel delivery from a selected outlet opening, the first and second valve needles being arranged adjacent to one another.
As fuel injection occurs when the valve needles are moved inwardly, the fuel injector provides the advantage that leakage during undesirable stages of the fuel injection cycle is substantially avoided. Furthermore, an improved fuel spray is achieved compared to fuel injectors of the outwardly opening type. By controlling the fuel pressure within the first and second control chambers so as to move one or both of the valve needles away from their respective seatings, the fuel injection rate, or other fuel injection characteristics, can be varied, in use.
Preferably, the first and second valve needles may be arranged substantially in parallel within the nozzle body.
Conveniently, the first control chamber may be arranged such that fuel pressure within the first control chamber serves to bias the first valve needle against the first seating and serves to bias the second valve needle away from the second seating. Conveniently, the second control chamber may be arranged such that fuel pressure within the second control chamber serves to bias the first and second valve needles against their respective seatings.
In use, fuel pressure within the first and second control chambers may be controlled such that, when fuel pressure within the first control chamber is held at a high level and the pressure within the second control chamber is reduced to a chosen low pressure, only the second valve needle moves away from its seating. Alternatively, when fuel pressure within the first chamber is reduced to a low level prior to reducing the pressure within the second control chamber to the chosen low level, only the first valve needle moves away from its seating. From either of these conditions, modification of the fuel pressure within the first control chamber may result in both valve needles occupying lifted positions.
It will be appreciated that the pressure within the first control chamber is used to select which of the needles will move, and the pressure within the second control chamber is used to control the timing of commencement and termination of injection.
The fuel injector may be constructed such that in use, when the fuel pressure within the first control chamber is at a relatively high level and fuel pressure within the second control chamber is reduced from a further relatively high level to a further relatively low level, only the second valve needle moves away from its seating to allow fuel to flow through the second outlet opening only.
Additionally, the fuel injector may be constructed such that, in use, when the second valve needle is lifted away from the second seating with fuel pressure within the first control chamber at the relatively high level, a reduction in fuel pressure within the first control chamber from the relatively high level to a relatively low level also causes the first valve needle to move away from the first seating.
Alternatively, or in addition, the fuel injector may be constructed such that, in use, when fuel pressure within the first control chamber is reduced from a relatively high level to a relatively low level, and fuel pressure within the second control chamber is subsequently reduced from a further relatively high level to a further relatively low level, only the first valve needle moves away from its seating.
The fuel injector may also be constructed so that in use, following a reduction in fuel pressure within the first control chamber to the relatively low level and the reduction of fuel pressure within the second control chamber to the further relatively low level, an increase in fuel pressure within the first control chamber to the relatively high level causes the second valve needle to lift away from the second seating.
The first and second valve needles may be guided for sliding movement by means of first and second bores respectively provided in the nozzle body, the first and second bores being arranged side by side and defining flow paths for fuel towards the outlets.
Alternatively, sliding movement of the first and second valve needles may not be guided. This provides the advantage that the nozzle body may be formed with an increased wall thickness to permit fuel at higher pressure to be delivered to the bore.
The nozzle body may be a unitary component or may comprise an upper nozzle body part provided with an opening and a lower nozzle body provided with first and second blind bores arranged side by side, the lower nozzle body part being received in the opening to close an open end thereof, the first and second blind bores receiving a respective one of the first and second valve needles and defining the first and second seatings respectively. The provision of a nozzle body having upper and lower parts provides a manufacturing advantage.
Conveniently, the nozzle body defines a delivery chamber for fuel. The first and second outlet openings may be provided in the nozzle body such that fuel delivery through the first and/or second outlet opening occurs when the first and/or second valve needle uncovers the respective outlet opening. Alternatively, the first and second outlet openings may be provided in the nozzle body such that the first and second outlet openings communicate with first and second sac regions respectively located downstream of the first and second seatings respectively, fuel delivery through the first and/or second outlet opening thereby taking place when the first and/or second valve needle is lifted away from its seating and fuel flows from the delivery chamber to the respective sac region.